Skylight Installation in Kelvedon

Kelvedon reads as two villages stacked on top of each other. There is the period high street, long and narrow, with rendered frontages and roof lines that step up and down as you walk it. Behind that, on the roads running off it, sits the commuter stock: post-war and later houses bought by people who wanted a mainline station and a garden. Those houses are where most of our work here happens, because they are the ones getting rear extensions with a roof lantern in the middle of the new flat roof.

It is 24.2 miles from Ipswich in a straight line, which in practice means 45 to 50 minutes down the A12 depending on how the Marks Tey stretch is behaving.

The lantern is the easy part. The structure under it is the job.

People choose a lantern from a picture. Fair enough, they look good. But the thing that decides whether it works for twenty years goes invisible once the plasterboard is up, and it is the kerb and the structure carrying it.

A roof lantern is heavy. Glass, aluminium rafter bars, a ridge, and on a decent sized unit that adds up quickly before you count wind load and, occasionally, snow. All of that weight arrives on a narrow rectangle of timber sitting on the flat roof deck. So the deck has to be designed around the opening from the start.

In practice that means three things:

• A ring beam or timber kerb sized for the load. Not an off-cut frame nailed round the hole. A continuous kerb, properly jointed at the corners, sized so it does not deflect between bearings.
• A steel or engineered beam where the opening spans wide. Once the lantern opening starts eating most of the width of a rear extension, the joists either side are carrying more than they were sized for. That is a structural calculation, not a judgement call on site.
• A dead level bearing. This is the one that catches people out, so it gets its own section.

Setting out square and level, to a few millimetres

An aluminium lantern is a rigid, factory-built object. It is square when it leaves the workshop and it stays square. If the kerb it lands on is twisted, so one corner sits five millimetres proud of the plane of the other three, the lantern cannot sit down evenly. The gasket compresses hard on two corners and hardly at all on the fourth. Water gets in at the corner that is not compressed, and it does it in driven rain.

So we set the kerb out with a laser and check the diagonals before anything is fixed. Square within a few millimetres, and level across all four sides, not just along the length. If the extension roof has a fall built into it, and it should have, that fall is taken up in the deck around the kerb rather than by tilting the kerb.

The thermal break at the kerb head

The kerb head is where the lantern frame meets the timber, and it is a natural weak point. Timber, then a metal frame, then cold outside air, with warm damp room air sitting underneath. Get it wrong and condensation runs down the inside face of the kerb in January, which people usually report as a leak because that is exactly what it looks like.

The fix is an unbroken line of insulation carried up the outside of the kerb to the underside of the lantern frame, a thermally broken frame on the unit itself, and the vapour control layer taken up the inside face and sealed. Done that way the kerb head stays above dew point. It is part of the detail we use for energy efficient skylight installation.

Sizing the lantern so it lines through with the room

A lantern has glazing bars, and they cast lines on the ceiling and the floor. If the bar spacing relates to nothing in the room below, it looks like an accident. We size the unit so the bars line through with something: the centre of an island, the line of a bifold post, the middle of the run. On a Kelvedon rear extension the usual arrangement is a lantern centred over the kitchen half, set out to that centre line rather than to the middle of the roof, which is often not the same point.

Lantern or flat glass rooflight?

They are not the same product and they do not suit the same house.

On the older properties near the high street a lantern often sits more comfortably with the house. On a clean-lined modern extension, a flat roof rooflight usually wins. If neither standard range fits the opening, that is what the custom skylight design service is for. Full detail is on roof lantern installation.

The glass in a lantern is a specification, not a given

A roof lantern is a large area of glass held up over a room, and on a south or west-facing kitchen extension that is a lot of sky pouring heat in on a summer afternoon. The lantern that looked perfect in spring can turn the room into a glasshouse by July if the glass is left as plain double glazing. So the glass is a decision, not a default.

• Solar control. A coating on the outer pane reflects a good part of the sun’s heat while still letting the light through, described by the g-value: a lower g-value means less solar heat gets in. On a bright-facing kitchen lantern it is usually money well spent, and it darkens the room barely at all.
• A laminated inner pane. Overhead glazing sits above people’s heads, so the sensible make-up puts a laminated pane on the inside, which holds together rather than falling as shards in the rare event it breaks. On a lantern over a kitchen table that is worth having as standard.
• A self-cleaning coating. A pitched lantern is exactly the glass you cannot reach to clean, sitting proud in the middle of a flat roof. A self-cleaning outer coating uses daylight and rain to break down and wash off the worst of the grime, which on an unreachable pitched surface is a practical help rather than a gimmick.

None of these change the structure under the kerb, which is still the real job. They change how the finished lantern performs once it is up there, and they are cheaper specified with the unit than regretted afterwards. The thermal side of the choice runs into energy efficient skylight installation.

A lantern does not drain itself

The pitched glass of a lantern sheds rain quickly, and all of that water lands on the flat roof around the kerb. If the extension roof does not carry it away cleanly, the lantern has simply concentrated the rain and dropped it at the foot of the kerb, which is the last place you want water sitting. So the flat roof around a lantern has to be designed to drain, with falls set out to move water past the kerb to an outlet, and on a larger extension a sensible arrangement includes somewhere for the water to go if the main outlet blocks with leaves. We set the falls out around the kerb as part of the work, the same principle used on any flat roof skylight installation, so the lantern and the roof it sits in are designed together rather than one dropped onto the other.

The high street is a different job from the estates behind it

Almost all our lantern work in Kelvedon is on the commuter stock behind the high street, where a modern rear extension is the natural host and permitted development usually covers it. The period high street itself is another matter. Its rendered frontages and stepped roof lines sit within the older part of the village, and where a property is listed or falls in a conservation area the rules that govern a rooflight or a lantern tighten considerably, consent rather than permitted development, and a flush conservation unit rather than a proud modern one. We check which side of that line your house sits on before we quote, because it changes both what is allowed and what suits the building.

Booking a skylight installation in Kelvedon

Every job is surveyed before it is priced, and the price is fixed in writing after that survey. Twenty-five years in the trade, a 10-year workmanship guarantee, installed to current Building Regulations. If your builder is still at foundation stage, that is the best time to get us involved, because the kerb can be designed in rather than retro-fitted.

We cover the same run of villages either side of the A12, including Coggeshall, Marks Tey and Tiptree. The full list is on areas we cover.

Request a fixed quote for a lantern or rooflight in Kelvedon. Send the extension dimensions and, if you have them, the structural drawings.